[en] There are a lot of problems for the direct detection of uranium in sea water, such as high salinity and complex matrix, and the uranium existing in sea water. Based on the theory of thermodynamics, by using PHREEQC for window simulation software for the existence form of uranium ion and influence factors in seawater was studied. Taking coastal water of Yangshan in Shanghai as an example, the form of uranium ions in water, the influence of acidity, the ionic strength on the uranium exist form was studied. Results shew that with pH = 8∼10 in the sea uranium was mainly existed as UO₂(CO₃)₃^4-. Uranium existing form in sea water is mainly affected by pH value, the influence of anion strength is not obvious. (authors)